This invention relates to an exhaust gas cleaning device for an outboard motor and more particularly to an improved catalytic treatment for the exhaust gases of an outboard motor.
Because of its compact nature, the design of outboard motors presents a number of problems peculiar to the specific application. The treatment of the exhaust gases in outboard motors is one such example where the design can present numerous problems due to the compact nature of the outboard motor.
With the intention of reducing the pollutants transmitted to the atmosphere from internal combustion engines, it has been proposed to employ catalytic exhaust systems for the outboard motor. These catalytic exhaust systems are particularly important since outboard motors frequently employ two cycle internal combustion engines and such engines may contain a fair amount of lubricating oil along with the other exhaust gas constituents typical with four cycle engines. Thus, catalytic converters are particularly advisable in treating the exhaust gases of outboard motors.
Generally the outboard motor is comprised of a power head in which the internal combustion engine is positioned and that engine has an exhaust manifold that discharges the exhaust gases downwardly into the drive shaft housing through an exhaust pipe. Various forms of silencing devices have been proposed in the drive shaft housing. For the most part, these exhaust systems must be quite compact due to the desire of maintaining a narrow profile for the drive shaft housing and particularly the portions that depends into the body of water in which the outboard motor is operating.
The exhaust gases are also discharged during high speed running through an underwater exhaust gas discharge for added silencing effect. This gives rise to certain problems, particularly when catalytic devices are used in the exhaust system. If any water can find its way back up through the exhaust system and impinge upon the catalyst, fracturing of the catalyst or deterioration of it can readily result.
For this reason, it has been proposed to position the catalytic bed at the upper portion of the drive shaft housing immediately adjacent the power head. With such an arrangement, however, the catalyst has been positioned in the exhaust pipe which delivers the exhaust gases from the engine. However, such positioning of the catalyst can cause restriction to the exhaust gas flow and adversely affect the power of the engine.
In order to avoid this restriction effect and to further protect the catalyst from the water which may enter through the underwater exhaust gas discharge, it has been proposed to provide a system where the exhaust pipe from the engine depends into an expansion chamber and a second exhaust conduit extends in part from the expansion chamber to the underwater exhaust gas discharge. This positioning of the catalyst with the type of constructions previously described has, however, somewhat restricted the size of the catalyst bed and thus problems still exist with this type of arrangement.
Frequently, the engine is also provided with banks of cylinders and for improved exhaust efficiency and exhaust gas tuning, it has been the practice to employ a separate exhaust pipe for each bank. This further complicates the problem of providing effective catalyst area and positioning.
It is, therefore, a principal object to this invention to provide an improved catalytic exhaust system for an outboard motor.
It is a further object to this invention to provide an improved catalytic system for the exhaust gases of an outboard motor wherein the catalyst is positioned where it will not be likely damaged from water entering the exhaust system through the underwater discharge and where the catalytic converter also has adequate cross sectional area to permit effective exhaust gas treatment without raising the exhaust restriction introduced by the catalyst.
It is a further object to this invention to provide an improved catalytic exhaust treatment system for an engine having banks of cylinders and two exhaust pipes.